1. Field of the Invention
The present invention relates to a piezoelectric oscillator having a resonator, which comprises a piezoelectric element, and a semiconductor integrated circuit apparatus, such as an IC or an LSI, which is connected to the resonator.
2. Description of Related Art
Piezoelectric oscillators formed by packaging a resonator and a semiconductor integrated circuit apparatus are classified into some types. A piezoelectric oscillator 10 shown in FIGS. 27(a) and 27(b) comprises a resonator 50 having a piezoelectric element, such as a quartz crystal resonator or a SAW resonator, sealed in a substantially cylindrical case 51; and an IC chip 60 in parallel to the resonator. The foregoing units are molded with molding resin 1 into a substantially rectangular shape so as to be formed into a surface-mounting plastic packaging type oscillator.
The piezoelectric oscillator 10 comprises a lead frame 70 having an island 71 which is molded into a plate-like shape and to which the IC chip 60 is secured by an electroconductive adhesive or the like. Electrodes 61 of the chip 60 and input/output leads 72 disposed around the island 71 are connected to one another by wire bonding lines 79. Two resonator leads 52 extend outside the case 51 that accomadates a quartz crystal resonator or a SAW resonator. The resonator leads 52 are connected to portions of the electrodes 61 of the IC chip 60 through connection leads 73 of the lead frame. The lead frame 70 that includes the resonator 50, the IC chip 60 and the leads for a variety of purposes is sealed by epoxy resin molding material 1 by a transfer molding method or the like so that an integrated piezoelectric oscillator is formed.
FIG. 28(a) and FIG. 28(b) show a piezoelectric oscillator 20, in which an IC chip 60, a lead frame 70 and a resonator 50 are sequentially laminated in the foregoing sequential order, and which is sealed into a substantially rectangular shape by a molding resin 1. Also in the foregoing piezoelectric oscillator 20, the IC chip 60 is secured to an island 71 by an electroconductive adhesive, and electrodes 61 of the chip 60 and respective leads are connected to one another by wire bonding lines 79 similarly to the foregoing piezoelectric oscillator 10. A case 51 of the resonator 50 is disposed on the island 71 opposite the IC chip 60, and resonator leads 52 extending from the case 51 are, connected to the IC chip 60 through connection lead 73. In the piezoelectric oscillator 20, the resonator 50, the IC chip 60 and the lead frame 70 are sealed by epoxy resin molding material 1 by a transfer molding method or the like, while stacked thereby reducing the area required for mounting to be accomplished.
However, the diameter of the cylindrical case is at least about 2 mm and, therefore, the overall thickness of the package is about 3.2 to 4.5 mm when considering the thickness of the lead frame 70 and the IC chip 60. Therefore, the height of the package sometimes raises a problem when the package is mounted on small and light electronic equipment or an OA apparatus, such as an FDD, an HDD, a domestic-use facsimile machine or a portable telephone.
Note that the structure of the IC chip and the resonator being disposed opposite each other on the island has also been illustrated in Japanese Patent Laid-Open No. 5-243471.
FIG. 29 shows a piezoelectric oscillator 30 which is not integrated by using the molding resin but in which an IC chip 60 and a quartz crystal resonator or a SAW resonator 53 are directly accommodated and packaged in a ceramic package 31. In the piezoelectric oscillator 30, the IC chip 60 is disposed on a bottom surface 32 of the ceramic case 31 so as to be, by a wire bonding lines 79, connected to a circuit (not shown) printed in the ceramic case. The quartz crystal resonator or the SAW resonator 53 is disposed on the IC chip 60 and are sealed by a metal or ceramic cover 39.
The foregoing piezoelectric oscillator has been employed as a clock source for use in electronic equipment, such as a computer. To meet the trend of the rising operation speeds of electronic equipment, the output frequency has been raised to a high region of about 50 MHz to 125 MHz. In recent years, piezoelectric oscillators each using a SAW resonator, that is capable of stably oscillating at high range frequencies, have been further realized, as well as oscillators each using a quartz crystal resonator. Oscillators of the foregoing type must stably maintain the high output frequencies of about 100 MHz to 500 MHz.
In proportion to the oscillation frequency, the electric power consumption of a semiconductor integrated circuit apparatus, such as an IC, for use in the piezoelectric oscillator is increased. The foregoing state is shown in FIG. 30. When the power supply voltage is 5 V for example, the piezoelectric oscillator consumes an electric current of about 38 mA if the frequency is 80 MHz, about 45 mA if the same is 100 MHz, and about 55 mA if the same is 125 MHz. These values are two to three times a values of about 10 mA to 17 mA of the conventional piezoelectric oscillator when its frequency output is about 20 MHz to 30 MHz.
It is well known that the heat generated by an IC is directly porportional to the power consumption of that IC. Since the heat generation of the IC is increased when the electric power consumption of the IC is increased, the temperature of the piezoelectric oscillator is undesirably raised. If the temperature in the piezoelectric oscillator is raised, the temperature of the junction portion in the IC is raised and, thus, portions of the IC are sometimes damaged. Additionally, characteristics of the IC are sometimes changed, which may adversely affect the reliability and the quality of the IC. If the temperature in the piezoelectric oscillator is raised to a level higher than the range in which the quartz crystal resonator or the SAW resonator, there sometimes arises a problem in that the accuracy of the oscillation frequency deteriorates and an abnormal frequency change takes place. If the piezoelectric oscillator is continuously operated in a state where the temperature is high, the reliability for a long time deteriorates due to accelerated aging.
Additionally, the size and thickness of the electronic equipment having the piezoelectric oscillator mounted thereon have been further reduced, and thus there arises a desire for reducing the size and thickness of the piezoelectric oscillator. Moreover, the oscillation frequency is raised, thus causing the heat generation of the IC accommodated in the smaller package to be increased. Therefore, the temperature in the package rises even more rapidly. It is necessary to overcome this problem of heat generation while providing a high quality piezoelectric oscillator capable of stable operation. Thus, heat generated in the package must be appropriately radiated.